When this thread started, I read it without thinking it had any relevance to me. Now I have a not-even-5-year-old horse who appears to be at the end of his performance career, and DSLD is a possibility. Pardon this long post but I want to share my experiences with the diagnostic process.
What I’ve found most interesting (and discouraging) is that even very knowledgeable vets cannot seem to agree on this topic. My horse has been seen by four extremely experienced lameness specialists and they have had a full range of opinions on him.
The first vet believes that he has suboptimal hind end conformation (long/“saggy” hind pasterns–which he distinguishes from “dropped” pasterns, which seem to happen over time as a result of a straight hind leg or DSLD) that will limit his career. He nevertheless recommended and performed a hind suspensory neurectomy, with the caveat that it is less likely to be successful in a horse with that conformation. When I specifically asked about DSLD, he told me not to worry about it. I believe that in his opinion, the hind end conformation is so limiting that it might as well be a DSLD diagnosis, as far as implications for the horse’s performance career, so he isn’t overly fussed about distinguishing one from the other. He also doesn’t have a lot of faith in the test (see below).
The second vet did not seem to have an opinion one way or another on DSLD when I asked, but she in turn asked the third vet, who has more experience with it.
The third vet (a very very big name) watched the horse walk a couple small figure 8’s and declared with certainty that he is a “breakdown horse.” I asked more questions to try to figure out what this means to him (long pasterns or DSLD?) and it seems he is certain the horse has DSLD. So certain that he thought a nuchal ligament biopsy wasn’t even necessary.
The fourth vet came into the picture while I was awaiting results of the biopsy so I’m not sure how strongly he feels about it but he did ask to be notified of the results. He agrees that the hind end conformation will probably preclude a performance career.
My point in all this is that knowledgeable vets can look at the same horse and see very different things. Some of them see obvious DSLD, others see a conformation issue. And these are top-notch lameness specialists. So imagine all the general-practice vets and non-vets out there looking at a horse with long or dropped pasterns, and it makes me wonder how many of those horses truly have/had DSLD and how many had suspensory desmitis, some other injury, “soft” pasterns, etc.
Another thing that bothers me is that my horse scored very well in in-hand classes through the American Hanoverian Society and in dressage sporthorse breeding classes at recognized shows. If vets can see that his hind end conformation is so horrible that he will never stay sound in work, why isn’t it being recognized by judges?
Now, as to the nuchal ligament biopsy… in talking to Vets #1-3, plus two other vets who did not see the horse in person but had some knowledge of DSLD, I also heard a range of opinions of the test.
Vet #1 doesn’t seem to have much faith in it. He cited Dr. Halper’s website, which says that a negative is a negative but a positive just means there are some signs consistent with the disease. He seems to find more value in examining the horse’s conformation and symptoms.
Vet #2 told me about a false negative she experienced where the diagnosis was confirmed as “very positive” on necropsy. Sounds like it may have been a lab error because when they re-examined the original nuchal ligament sample, they decided it was positive after all.
Vet #3 blew off the false negative, saying it was “just one.” When I asked what their sample size was, I was shocked to hear that this practice has only biopsied 8 or 9 horses. So they have experienced a false negative rate of over 10% and he apparently still thinks this test is infallible. By the way, this is only 8 or 9 tests over about a decade, so the test is just not that common.
Vet #4 didn’t express an opinion about the test and I didn’t ask, as I had already done it and was awaiting results when I saw him.
Vets #5 and 6 had no firsthand experience with the biopsy but one had co-authored a study on diagnosing DSLD in Pasos based on skin enzymes, so at least she has some knowledge of the disease. They were both willing to perform the biopsy but skeptical of its value. One pointed out that there hasn’t been a single peer-reviewed paper on it yet, which is a compelling point. The original EPSA paper is 12 years old now (https://bmcvetres.biomedcentral.com/…1746-6148-2-12) and there is very little published research on the disease and none on the biopsy itself.
I decided to do the biopsy because it is relatively inexpensive and a positive result would be so devastating (although maybe it is not actually that clear). It was not a procedure for the faint of heart. (I recall in some other thread about DSLD somebody saying that a nuchal ligament biopsy would be an awkward request on a PPE and I can tell you that “awkward” doesn’t even begin to describe it! I don’t see any seller in the world consenting to this.) They obviously have to cut rather far into the neck to reach the nuchal ligament, and then they exert significant force to hold it still and carve out a chunk. My horse was heavily sedated and still jumped when it was cut. The area around the incision site puffed up nastily that evening (see pic) and he seemed to be in pain. He wasn’t his usual happy-go-lucky self and seemed ouchy when I tried to elevate his head to dose him with bute (which the vet didn’t think was needed but I felt terrible for him and hoped it would help). I was really regretting putting him through the whole thing for a test of questionable value. It looks better now and thankfully his attitude bounced back after a day or two. I think there may be scarring on a very visible part of his beautiful neck, but since he is literally three-legged lame I suppose that doesn’t matter much anymore. 
I should have the biopsy results any day now and will update then.
Sorry for the long post but I hope it’s helpful to anyone else going through this.
